This invention relates generally to the synthesis and polymerization of phthalonitrile monomers, and, more particularly to the synthesis, polymerization and pyrolization of dithioether-linked phthalonitrile monomers.
Phthalonitrile monomers have two phenyl dinitrile groups connected by a linking group. The linking group in the monomer becomes the linking group in the polymer. The properties of the polymer are determined to a large degree by the linking group. Heretofore, the linking group has been generally hydrocarbons, phenoxy, alkoxy or sulfone moieties.
Examples of previous phthalonitrile monomers and polymers demonstrate the versatility and importance of this growing class of materials. Keller, in the U.S. Pat. No. 4,234,712, used sulphone and ketone groups to link phthalocyanines, thus forming high temperature structural composites and adhesives. Similarly, Keller, in U.S. Pat. No. 4,238,601, used perfluorinated alkyl substituents on the linking and phenyl groups to increase the corrosive resistance of polymerized phthalocyanines. Polyphenylether-bridged polyphthalocyanines were prepared by Keller, U.S. Pat. No. 4,259,471, which exhibited exceptional thermal stability and oxidative resistance. Also, by varying the fluoride content of the constituent and substituent groups of the linking group, Keller, in U.S. Pat. No. 4,315,093, produced a phthalonitrile polymer with improved water repellancy and resistance to oxidative attacks. The performance of the polymers have exceeded polyoxides, epoxies and other similar polymers in many applications.
One property of high-temperature organic materials that is of great interest is electrical conductivity. Materials with high conductivities have been obtained by either chemical doping of a linear conjugated system or by thermal treatment of polymers. In the case of chemical doping, the conductivity of a polymer is varied and controlled by the amount of dopant used. For thermal treatment, the conductivity of a polymer is changed by a precise pyrolytic procedure. One polymer that has produced a highly conductive organic material through thermal treatment is the diether-linked phthalonitrile polymer of U.S. Pat. No. 4,587,325. It has been determined that the ether linkages interrupt electronic delocalization. Hence a pyralyzed polymer without ether linkages would have a better electrical stability.